Sources tell me that Microsoft plans to launch a new Surface Pro model on Tuesday that is both bigger and thinner than the current Surface Pro 2. Beyond that, I don't have too many new details, but I'm wondering whether the new device is an additional model and not a replacement for Surface Pro 2.

What I'm hoping for—and I did layout a more detailed version of this in Surface Family Grows: Mini, Sure, But How About Maxi Too?—is something that is at least as thin as a Surface 2 (the RT-based model) but with a bigger screen. In that article, I tried to temper my wants/needs with an acknowledgment that Surface devices are somewhat limited—or perhaps "laser focused"—to addressing a presumed market for tablet-based mobile computing devices. But on the flipside, I think it's also worth noting that Microsoft under new CEO Satya Nadella seems to be reassessing everything it does. So it's possible that the Surface strategy could be evolving as well.

The problem is, as you make a tablet (or a transforming, tablet-like device such as the Lenovo Yoga line) bigger, it becomes less useful as a tablet. The Yoga 2 Pro I recently reviewed is an absolutely wonderful device ... as a laptop. But when you fold the screen back and use it like a tablet, it's big and heavy. And as bad, the widescreen display appears oddly "tall" when used in portrait mode. There's just something weird about this configuration.

I don't expect to see a 4:3 Windows tablet anytime soon, but as many have noted here in the comments, such a device would be wonderful and appreciated. It's unlikely that the new Surface Pro, which I'll call Surface Pro Book for now, is such a device.

So what's reasonable to expect?

We know Surface Pro Book will be powered by a current generation Intel Core "Haswell" processor, and that there will in fact be a range a processor choices. It's a Pro device, not a consumer device.

We know it will run "real" Windows 8.1, not Windows RT.

We know it will be bigger and thinner. But not how much bigger and how thin. It's not hard to imagine "squashing out" the current Surface Pro 2 so that it is both bigger and thinner but has the same overall battery capacity, and I am OK with that. But the size. I'm curious about the size.

The Yoga 2 Pro has a 13-inch screen, which again is semi-ideal in laptop mode but too big in tablet mode. My guess is that Surface Pro Book is not some new concoction but is rather something the Surface team has been working on since at least last year. So it's probably not all that radical from a design standpoint.

How big is too big? 13 inches. But what about 12 inches? 12.5 inches?

How about a device that maximizes the screen size within the body of the device and eschews a large bezel? You could easily fit a bigger screen in the existing Surface Pro 2 if you just gave up .25 to .5 inches on each bezel. Imagine how big the screen could be in a device that was just an inch bigger in each dimension.

Whatever this device is, I'm interested. The current Surface Pro 2 is just too small for me, and too small for what I think constitutes a Pro device. (Yes, opinions vary.) A bigger device would better serve what I believe to be the prime directive for Windows—productivity first—and in particular that Pro audience: People who need to type every day, like IT pros, office workers, business travelers, developers, and more. There are devices that are just a hair bigger than the Surface Pro 2—like the Dell Venue 11 Pro—that are much better for this audience from a form factor perspective, so it's not surprising that the idea of a bigger Surface Pro is enticing.

Fingers crossed.

PS: It's become clear that some misinformation about Tuesday's event has been seeded in an attempt, I think, to find leakers. To try and combat these efforts, I've relied on multiple sources and have not published information when it's arrived. I appreciate and respect the Surface team's desire to tell their own story. But aside from the normal Fourth Estate stuff, I get regular questions of the "should I wait to buy?" variety. Of course you should. It's just a few more days.